Crystal structure and spectroscopic characterization of a green VIV compound, Na8(VO)2(SO4)6

Abstract

A mixture of green crystals was precipitated at 467°C from around 1.5 mL of a melt, consisting of Na2S2O7 and V2O5 in the molar ratio Na/V=4. The melt was in contact with a 10% SO2-90% N2 mixed gas atmosphere. A minor amount of the product consisted of the green VIII compound NaV(SO4)2, previously investigated. The majority consisted of another kind of crystal, whose X-ray structure is reported here. The obtained formula was Na8(VO)2(SO4)6, crystallizing in the monoclinic space group P21/c, with a = 8.6454(2), b = 16.0027(4), c = 15.5074(4) Å and β = 90.017(1)° at 22°C and Z = 4. Surprisingly the crystals were not blue as would be expected from the +4 oxidation state of the vanadium. The structure consists of two kinds of octahedrally coordinated vanadium atoms, each closely bound to an O2- (forming the vanadyl group VO2+) and five sulfato groups, the one trans to oxide at a longer distance. A complicated 3-dimensional network of V-O-SO2-O-V bonding is described, in between which the Na+ ions are found. Infrared and Raman spectra of the compound were obtained and assigned to modes of the sulfato and vanadyl ions, but many fewer fundamentals were found than prescribed by the factor group analysis based on the unit cell. Copyright © Acta Chemica Scandinavica 1999.